pressures, which soon reach their limit in cylindrical boilers;
so, stated briefly, a less economical boiler is adopted to secure
a more economical engine. It is a mistake to suppose all water-
tube boilers fit for forcing:, the following classifies the principal
types regarding this quality:—
LIST OF TYPICAL WATER-TUBE BOILERS.
For Natural Draught only.
Capable of some Forcing.
For Forced Draught.
The four last-mentioned are most suitable for fast-speed war
vessels, such as ' destroyers,' which require increased combustion
The Babcock-Wilcox boiler has been already described, and
n|ay be taken as a type of natural-draught boiler. , The Ntdamse